1. Field of the Invention
The present invention relates to two new strains of Bacillus thuringiensis (the "BTS02584B and BTS02584C strains") which produce crystal proteins (the "BTS02584B and BTS02584C crystal proteins") which are packaged in crystals (the "BTS02584B and BTS02584C crystals") during sporulation.
The present invention also relates to an insecticide composition that is active against Coleoptera, more particularly against Diabrotica species(hereinafter abbreviated "spp.") which comprises sporulated cultures of the BTS02584B or BTS02584C strains or the active component(s) thereof as an active insecticidal ingredient.
The present invention also relates to a method for combatting Diabrotica pests by contacting these pests with BTS02584B and/or BTS02584C strains, sporulated cultures of the BTS02584B and/or BTS02584C strains or with their insecticidally effective component(s).
2. Description of the Prior Art
Some of the most destructive pests are found among the Diabroticina beetles. In North America, the three important species of corn rootworms, Diabrotica virgifera virgifera (the Western corn rootworm), Diabrotica barberi (the Northern corn rootworm) and Diabrotica undecimpunctata howardi (the Southern corn rootworm) are considered to be the most expensive insect pests to control (Metcalf, 1986). Diabrotica virgifera virgifera and Diabrotica barberi are considered the most serious insect pests of corn in the major corn-producing states of the United States and Canada (Levine and Oloumi-Sadeghi 1991). The larvae feed on the roots and thus cause direct damage to corn growth and corn yields. Costs for soil insecticides to control larval damage to the root systems of corn and aerial sprays to reduce beetle damage to corn silks, when combined with crop losses, can approach one billion dollars annually (Metcalf, 1986).
B. thuringiensis is a gram-positive bacterium which produces endogenous crystals upon sporulation. The crystals are composed of proteins which are specifically toxic against insect larvae. Three different Bt pathotypes have been described. Pathotype A that is active against Lepidoptera; pathotype B that is active against certain Diptera, e.g., mosquitoes and black flies; and pathotype C that is active against Coleoptera, e.g., beetles (Ellar et al., 1986). The fact that conventional submerged fermentation techniques can be used to produce Bt spores and sporulated cultures on a large scale makes Bt bacteria commercially attractive as a source of insecticidal compositions.
A Bt strain, whose crystals are toxic to Coleoptera, has been described as Bt tenebrionis and BTS1 in U.S. Pat. No. 4,766,203; European Patent Publication No. 0,213,818; U.S. Pat. No. 4,771,131; and European Patent Application No. 88/402,115.5. Subsequently, other Coleopteran-active strains have been isolated as described in PCT patent publications WO 91/00791 and WO 90/09445. The Bt tenebrionis strain which carries the Coleopteran-active cryIIIa gene has been reported to kill a variety of Coleoptera. However, according to Slaney et al (1992) the toxin encoded by this gene was found to be much less effective to Diabrotica larvae than to the Colorado potato beetle, Leptinotarsa decemlineata. Diabrotica was found to have a poor ability to bind the CryIIIA toxin.